Most current dot or wire matrix printing mechanisms have complicated and cumbersome transport designs for advancing the print head, paper, and ribbon of the mechanism. Few, if any, transport systems are designed with simplicity, ease of assembly and repair, and low cost in mind. The transport system of the present invention, however, was designed to have just such qualities and to appeal particularly to the developing personal and small business computer markets.
Special attention was directed during the design of the current invention to using snap fits throughout the assembly rather than screws, to reducing the number of free parts by making as many parts integral with each other as possible and having parts perform multiple functions wherever possible, and to using the same part design wherever possible for improved dynamic balance and lower cost. Special attention was also directed to reducing the complexity of the power train by making all of the moving parts of the transport system interconnected and driven off a single motor through a common drive train, to making a ribbon cartridge assembly and support whereby the ribbon traveled on a bias to increase its life, and to reducing the overall size of the mechanism, as for example, by mounting the main body of the ribbon cartridge on the opposite side of the platen from the print head. In certain instances, new individual elements of the transport system were designed such as a new feed pawl arrangement for advancing the paper, new cam-follower arrangement for the print head, and new bearings for supporting the rotating shafts of the transport system.
With the overall design of the transport system of the present invention, only nine screws are needed for assembly and assembly time is measured in fractions of an hour (e.g., ten minutes) rather than multiples of hours as is the case with comparative systems. Further, the overall design significantly reduces the complexity and time of any repair work as the current transport system can be disassembled and reassembled in about a fifteen minute period representing a distinct advantage over existing systems.